Offshore hydrocarbon production systems generally include a plurality of wells extending to undersea deposits of oil, with trees located on the sea floor, wherein each tree includes a plurality of valves and pipe couplings. Risers extend up from the trees to apparatus floating at the sea surface that has oil handling equipment. One low-cost production apparatus comprises a spar buoy or spar in the form of a body having a height that is a plurality of times its average width, and usually at least 5 times as tall as wide. The small width of the spar results in only moderate drift in reaction to winds, currents, and waves, which results in only moderate bending of the risers and fluid-carrying pipes therein. To keep the spar upright, its upper portion is made highly buoyant while its lower portion contains considerable ballast to weight it and thereby lower its center of gravity. There are several occasions when it would be desirable to disconnect a spar buoy from the risers that extend down to the sea floor. Some of these include disconnection when icebergs approach, and disconnection to permit use of a workover vessel such as a semi-submersible platform that carries pipes that can extend to the tree to carry tools to clean out wax deposits. In deep seas, expensive workover vessels must be used, with conduits that can extend down to trees at the sea floor. An offshore hydrocarbon production system that facilitated installation of the spar and its disconnection, especially to enable a workover vessel to work on the risers, trees and undersea pipes, would be of value.